1. Field of the Invention
The present invention relates to traffic signals, in particular light emitting diode (LED) traffic signals. More specifically, the present invention relates to a count down pedestrian traffic signal that incorporates a cost and energy efficient switching power supply with power factor correction circuitry to drive both logic circuits and the various LED arrays.
2. Description of the Related Art
Pedestrian signals which indicate the time remaining before signal change are well known. Models incorporating an audible tone which increases in frequency as time runs out have been used as well as illuminated digit count down signals including pictograms indicating a walk (walking man) and/or don""t walk (hand) symbol. Previous count down signals using LEDs benefited from the increased energy efficiency and extended maintenance interval of the LED as the illumination source. However, these signals use two separate power supplies for the pictograms and for the count down display. Until now, these power supplies have been of linear design. Linear power supplies suffer from high power consumption overall and poor power factor resulting in especially high reactive power consumption.
A typical linear power supply used in a comparable LED count down signal consumes 60 VA while the present invention utilizing switching power supplies consumes 25 VA. Normally, switching power supplies are not used where logical circuits are in close proximity. This is because switching power supplies inherently create electronic noise. This electronic noise is enough to disrupt logic circuits used to drive the count down arrays. The present invention solves this problem. Integration of the switching power supplies and logic circuits supplies a further materials efficiency thereby resulting in the present invention having both a lower cost of manufacture and a lower cost of operation due to the higher energy efficiency.
Further objects will be realized by one skilled in the art, through review of the following description and appended claims.
The present invention has a Printed Circuit Board (PCB) populated by multiple arrays of LEDs. The LEDs may represent the pictogram of a hand indicating that pedestrians should not cross and a man walking indicating crossing is permitted. Another set of LED arrays make up digits for a numeric display. The digits show the time remaining and by viewing the change of the digits, the rate of time passage. An isolated interface is provided to receive signals from the intersection traffic lights which set the mode of the count down signal. Separate Power Supply Units (PSU) are used for the count down digits as compared to the hand and man arrays. Electronic noise filtering is applied to the power inputs of the PSU""s. Further noise suppression is created by configuration of separate ground planes maintained on the Printed Circuit Board (PCB) with only a single connection point between the power supply circuitry and the logic circuitry.